The invention relates to a device as well as to a method for processing flat substrates such as for printing circuit boards or the like.
To enable a flat substrate to be processed, it has to be disposed in the device in a certain position. When doing so, it is particularly important that the surface of the substrate which is to be processed is flat and without any warps, bend-ups or the like. This is particularly important when printing circuit boards by means of the usual printing devices (using screen printing).
Typically, the flat substrate is fed into the device by means of a transport device by two oppositely facing lateral edge areas, is processed there and is transported away after processing by means of a similar transport device (cp. e.g. DE 101 17 873 A1). In the case of somewhat thicker substrates, in particular circuit boards having a high inherent rigidity, it may occur that the corner areas bend upwards and/or that, particularly in the case of loaded or partially loaded circuit boards, some transverse or longitudinal warpage is present in the flat substrate supplied. In order to enable the processing, in particular the printing to be carried out, such bend-ups or warpages need to be removed. To this end the supplied substrate, once it reaches the processing position, is moved in the device from the bottom upwards by means of supports against lateral hold-downs, whilst the warpage or bend-up is compensated by means of the pressure applied. In this position, corresponding clamping bars will then be moved against the oppositely facing lateral edges, with the clamping force being sufficient to keep the inherently rigid substrate between them, and this in such a way that the warps and bend-ups mentioned will not reappear even after the hold-downs have been removed. Subsequently, the processing, for example the printing process, will be carried out. If the hold-downs are completely removed from the area of the substrate, a printing process even across the entire surface may be carried out.
In the case of thinner substrates having a comparatively low inherent rigidity, the above-mentioned problems will not occur, but the application of clamping forces would rather result in a bending of the substrate. According to the DE 101 17 873 A1, the substrate transported to the processing position will initially be deposited on supports by its edges and any clamping bars provided will essentially not be used for applying a clamping force, which of course is to be avoided, but for a lateral alignment and for retaining its position. Here, too, the flat substrate will then typically be supported by means of supports moving from the bottom upwards, but it cannot be entirely processed, particularly not be printed across its entire surface.
Therefore there is a need, also in the case of thin substrates where clamping forces may be applied, if necessary, only to a very minor extent, preferably not at all, to enable flat substrates to be processed or printed across their entire surface, whilst their flat disposal is maintained.